Radio base station apparatus, mobile terminal apparatus, radio communication system and radio communication method

ABSTRACT

The present invention is designed to provide a radio base station apparatus, a mobile terminal apparatus, a radio communication system and a radio communication method which can cope with an increased number of users. A radio base station apparatus is provided with: a signal generating section that generates a first downlink control signal and a second downlink control signal for a mobile terminal apparatus; a first multiplexing section that multiplexes the first downlink control signal on a control region up to a predetermined number of symbols from the top of a subframe; a second multiplexing section that frequency-division-multiplexes the second downlink control signal on radio resources from the next symbol in the control region to the last symbol of the subframe; and a transmission section that transmits the first downlink control signal multiplexed on the control region and the second downlink control signal multiplexed on the radio resources.

TECHNICAL FIELD

The present invention relates to a radio base station apparatus, amobile terminal apparatus, a radio communication system and a radiocommunication method in a next-generation radio communication system.

BACKGROUND ART

In the UMTS (Universal Mobile Telecommunications System) network, forthe purposes of further increasing high-speed data rates, providing lowdelay and so on, long-term evolution (LTE) has been under study (see,for example, non-patent literature 1). In LTE, as multiple accessschemes, a scheme that is based on OFDMA (Orthogonal Frequency DivisionMultiple Access) is used on the downlink, and a scheme that is based onSC-FDMA (Single Carrier Frequency Division Multiple Access) is used onthe uplink.

Also, for the purpose of achieving further broadband and higher speedbeyond LTE, a successor system of LTE has been under study. Thissuccessor system may be referred to as “LTE advanced” or “LTEenhancement” (hereinafter referred to as “LTE-A”). In LTE (Rel. 8) andLTE-A (Rel. 9 and Rel. 10), MIMO (Multi-Input Multi-Output) techniquesto improve spectral efficiency by transmitting and receiving data by aplurality of antennas are under study as a radio communicationtechnique. In the MIMO system, a plurality of transmitting/receivingantennas are provided in the transmitter/receiver, so that differenttransmission information sequences are transmitted from differenttransmitting antennas, at the same time.

CITATION LIST Non-Patent Literature

Non-Patent Literature 1: 3GPP TR 25.913 “Requirements for Evolved UTRAand Evolved UTRAN”

SUMMARY OF INVENTION Technical Problem

Now, in LTE-A, multiple-user MIMO (MU-MIMO) to transmit transmissioninformation sequences to different users from different transmittingantennas at the same time is defined. This MU-MIMO transmission is alsostudied for application to a HetNet (Heterogeneous Network) and CoMP(Coordinated Multi-Point) transmission. Consequently, in future systems,the number of users to be connected to a base station apparatus isexpected to increase, and there is a threat that the downlink controlchannel capacity runs short.

The present invention has been made in view of the above, and it istherefore an object of the present invention to provide a radio basestation apparatus, a mobile terminal apparatus, a radio communicationsystem and a radio communication method which expand a downlink controlchannel to increase its capacity and make it possible to multiplex moredownlink control information (DCI).

Solution to Problem

A radio base station apparatus according to the present invention has: asignal generating section that generates a first downlink control signaland a second downlink control signal for a mobile terminal apparatus; afirst multiplexing section that multiplexes the first downlink controlsignal on a control region up to a predetermined number of symbols fromthe top of a subframe; a second multiplexing section thatfrequency-division-multiplexes the second downlink control signal onradio resources from the next symbol in the control region to the lastsymbol of the subframe; and a transmission section that transmits thefirst downlink control signal multiplexed on the control region and thesecond downlink control signal multiplexed on the radio resources.

A mobile terminal apparatus according to the present invention has: areceiving section that receives a first downlink control signal that ismultiplexed on a control region up to a predetermined number of symbolsfrom the top of a subframe and a second downlink control signal that isfrequency-division-multiplexed on radio resources from the next symbolin the control region to the last symbol of the subframe; a channelestimation section that performs channel estimation for the receivedfirst downlink control signal using a cell-specific reference signal,and performs channel estimation for the received second downlink controlsignal using the cell-specific reference signal or a user-specificreference signal; and a demodulation section that demodulates the firstdownlink control signal and the second downlink control signal usingchannel estimation results.

Advantageous Effects of Invention

According to the present invention, a downlink control channel isenhanced to increase its capacity, so that it is possible to multiplexmore DCI.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a HetNet where MU-MIMO is applied;

FIG. 2 is a diagram to show an example of a subframe where downlinkMU-MIMO transmission is performed;

FIG. 3 is a diagram to explain an enhanced PDCCH (FDM-type PDCCH);

FIG. 4 is a diagram to show an example of allocation of an enhancedPDCCH to a system band;

FIG. 5 provides diagrams to explain examples of a search space when theenhanced PDCCH format is “with cross interleaving;”

FIG. 6 is a diagram to explain an example of a search space when theenhanced PDCCH format is “without cross interleaving;”

FIG. 7 provides diagrams to show examples of an FDM-type PDCCH resourceblock;

FIG. 8 is a diagram to explain cross-carrier scheduling;

FIG. 9 is a diagram show and explain an example of applyingcross-carrier scheduling to an FDM-type PDCCH;

FIG. 10 is a diagram to explain a system configuration of a radiocommunication system;

FIG. 11 is a diagram to explain an overall configuration of a basestation apparatus according to the present embodiment;

FIG. 12 is a block diagram to show an overall configuration of a mobileterminal apparatus according to the present embodiment;

FIG. 13 is a functional block diagram of a baseband signal processingsection provided in a base station apparatus according to the presentembodiment, and part of higher layers; and

FIG. 14 is a functional block diagram of a baseband signal processingsection provided in a mobile terminal apparatus.

DESCRIPTION OF EMBODIMENTS

FIG. 1 is a schematic diagram of a HetNet where MU-MIMO is applied. Thesystem shown in FIG. 1 is configured in layers by providing a micro basestation apparatus RRH (Remote Radio Head) having a local cell in thecell of a base station apparatus eNB (eNodeB). In downlink MU-MIMOtransmission in such a system, not only transmitting data to a pluralityof mobile terminal apparatus UEs (User Equipment) from a plurality ofantennas of a base station apparatus eNB at the same time, but alsotransmitting data for a plurality of mobile terminal apparatus UEs froma plurality of antennas of a micro base station apparatus RRH at thesame time is expected, and therefore there is a possibility thatdownlink control channel capacity runs short.

Also, in a Hetnet where CoMP is applied, there is a possibility toperform cell range expansion dynamically, while a mobile terminalapparatus UE is connected to a macro base station apparatus eNB. In thiscase, a mobile terminal apparatus UE that is located near the cell edgeof the micro base station apparatus RRH receives downlink controlsignals from the base station apparatus eNB and receives downlink datasignals from the micro base station apparatus RRH. Consequently, thedownlink control channel capacity in the base station apparatus eNB mayrun short. To solve this problem, although a configuration to transmitdownlink control signals from the micro base station apparatus RRH maybe possible, the micro base station apparatus RRH has limited downlinkcontrol channel capacity.

Like the above-described configuration, although the spectral efficiencyis improved by MU-MIMO, the problem that the downlink control channelcapacity of the base station apparatus eNB runs short may arise. FIG. 2is a diagram to show an example of subframe where downlink MU-MIMOtransmission is performed. In the subframe, a signal of downlink datafor a mobile terminal apparatus UE and a signal of downlink controlinformation for receiving that downlink data aretime-division-multiplexed and transmitted.

A predetermined number of OFDM symbols from the top of the subframe aresecured as a resource region (PDCCH region) for a downlink controlchannel (PDCCH: Physical Downlink Control CHannel). The PDCCH region isformed with maximum three OFDM symbols from the top of the subframe, andthe number of OFDM symbols changes dynamically per subframe (that is,the number of OFDM symbols is selected from 1 to 3), depending ontraffic information (for example, the number of users to be connected).The radio resource region (PDSCH region) for a downlink data channel(PDSCH: Physical Downlink Shared CHannel) is secured in radio resourcesafter a predetermined number of symbols from the top of the subframe.

Furthermore, in the PDCCH region, DCI to correspond to each mobileterminal apparatus UE is allocated. However, cases might occur where, inthe PDCCH region that is formed with maximum three OFDM symbols from thesubframe top alone, DCI for all of the mobile terminal apparatus UEscannot be allocated. For example, in the example shown in FIG. 2, thePDCCH region runs short due to increased DCI, and it is not possible tosecure resources to allocate downlink control information for mobileterminal apparatus UEs #5 and #6. In this way, in a radio communicationsystem where MU-MIMO transmission is applied, resources to allocate DCImay run short, and the influence against the throughput performance ofMU-MIMO transmission poses a problem.

To solve this shortage of the PDCCH region, it may be possible to expandthe PDCCH to outside the maximum three OFDM symbols from the top of asubframe (that is, expand the PDCCH to the existing PDSCH region).According to the first aspect of the present invention, a frequencydivision multiplexing-type PDCCH is set in radio resources that are apredetermined number of symbols after the top symbol of a subframe,downlink control signals are arranged in the FDM-type PDCCH, and thedownlink control signals and downlink data signals aretime-division-multiplexed and transmitted to a mobile terminal apparatusUE.

FIG. 3 is a diagram to show a subframe configuration, in which anconventional PDCCH and an FDM-type PDCCH are arranged. In several OFDMsymbols (the first to third OFDM symbols) from the top of a subframe, aconventional PDCCH is arranged over the entire system band, and, inradio resources after the symbols where the conventional PDCCH isarranged, the FDM-type PDCCH is arranged. The bandwidth of one FDM-typePDCCH in the frequency domain is the size of the radio resourcescheduling unit—for example, one resource block (RB).

In this way, by supporting the FDM-type PDCCH as an enhanced PDCCH bythe downlink for transmitting downlink control signals from the basestation apparatus eNB to the mobile terminal apparatus UE, it ispossible to use a predetermined frequency region of a conventional PDSCHregion as an enhanced PDCCH region. The enhanced PDCCH region can bedemodulated using a user-specific DM-RS (DeModulation-Reference Signal)that is arranged in the conventional PDSCH region. The DM-RS is definedas a UE-specific reference signal and can be subjected to beam formingseparately between UEs, so that sufficient received quality can beachieved. Consequently, even for UEs near the cell edge, it is possibleto decrease the aggregation levels as long as the communicationenvironment is good, so that it is possible to improve throughput.

Here, the method of allocating an enhanced PDCCH (FDM-type PDCCH) to thesystem band will be described with reference to FIG. 4. Note that FIG. 4shows a case where eight (N_(VRB)=8) virtual resource block (VRB) setsare configured as an enhanced PDCCH, in a cell bandwidth formed withtwenty-five physical resource blocks (PRBs). Also, FIG. 4 shows a casewhere the resource allocation type is 0 (resource allocation type 0).Obviously, the present invention is not limited to this.

As resource block allocation types, there are three different types(resource allocation types 0, 1 and 2). The resource block allocationtypes 0 and 1 support discontinuous frequency arrangement in thefrequency domain, and the type 2 supports only continuous frequencyarrangement. The resource block allocation type 0 is represented inunits of groups of neighboring resource blocks, not in units ofindividual resource blocks in the frequency domain, thereby reducing thebitmap size. In FIG. 4, the cell bandwidth is formed with twenty-fiveresource blocks, so that the size of a resource block group (RBG) istwo. In this case, eight VRB sets are arranged in PRBs (RBGs=1, 3, 7 and8) in units of two.

The base station apparatus eNB reports N_(VRB) VRB sets to the mobileterminal apparatus UE, by higher layer signals, as an enhanced PDCCH.When configuring as shown in FIG. 4, predetermined RBGs (here, RBGs=1,3, 7 and 8) are reported to the mobile terminal apparatus UE. Also, theVRBs are numbered by VRB indices, in order, from the smallest PRB index(RBG index).

The resource blocks of the enhanced PDCCH may assume a configuration toarrange downlink control signals separately between the first-half slot(first slot) and the second-half slot (second slot). Also, as enhancedPDCCH formats, there are a method of allocating each user's downlinkcontrol signal in control channel element (CCE) units, which are formedwith a plurality of resource element groups (REGs) (“with crossinterleaving”), and a method of allocating each user's downlink controlsignal in PRB units (“without cross interleaving”).

In the event of “with cross interleaving,” the mobile terminal apparatusUE performs blind decoding in search spaces defined by CCE indices, and,in the event of “without cross interleaving,” the mobile terminalapparatus UE performs blind decoding in search spaces defined by VRBindices. Now, blind decoding in each format will be described below.

<With Cross Interleaving>

In the event of “with cross interleaving,” the base station apparatuseNB assigns CCEs, which are formed with continuous REGs in radioresources that are available for use, to an enhanced PDCCH. Note thatone CCE is formed with nine REGs. Also, one REG is formed with fourresource elements. For example, the base station apparatus eNBdetermines aggregation levels (aggregation levels Λ (=1, 2, 4, 8)),which represents the number of CCEs to allocate continuously, based onthe received quality reported from each mobile terminal apparatus UE.Then, in the enhanced PDCCH, the base station apparatus eNB sets REGs tomatch the number of CCEs corresponding to the aggregation level of eachmobile terminal apparatus UE.

For example, when eight (N_(VRB)=8) VRB sets are arranged as an enhancedPDCCH in the resource allocation type 0 to a cell bandwidth formed withtwenty-five PRBs, REGs are arranged in the radio resources of the PRBsas shown in FIG. 5A.

Nine REGs to constitute one CCE are allocated continuously in thefrequency domain, to the radio resources of the VRBs constituting theenhanced PDCCH. As shown in FIG. 5B, one CCE is formed with nine REGsthat are allocated in the frequency direction of the continuous VRBsets. Note that, in the radio resources of the VRBs, where there areresource elements to be allocated as reference signals such as CRSs,REGs are allocated to avoid these resource elements. Also, based on theaggregation level of each mobile terminal apparatus UE, the base stationapparatus eNB allocates continuous CCEs to the enhanced PDCCH signal ofeach mobile terminal apparatus UE.

The mobile terminal apparatus UE monitors a plurality of enhanced PDCCHcandidates that may be set by higher layer signals. This is referred toas blind decoding. The mobile terminal apparatus UE is not reported theCCEs where the enhanced PDCCH signal for the mobile terminal apparatusUE is allocated, and the selected aggregation level. Consequently,enhanced PDCCH decoding is executed for all the CCEs where the enhancedPDCCH signal for the mobile terminal apparatus UE may be allocated.

Also, to minimize the number of times the mobile terminal apparatus UEtries blind decoding, the base station apparatus eNB sets a search spacefor every mobile terminal apparatus UE, and is able to allocate CCEs forthe enhanced PDCCH signal for each mobile terminal apparatus UE in thissearch space. In this case, the mobile terminal apparatus UE tries todecode the enhanced PDCCH in the corresponding search space.

When trying blind decoding in the search space, the mobile terminalapparatus UE is able to determine the search space by the followingequations 1, according to each aggregation level. Note that the numbersof PDCCH candidates to correspond to individual aggregation levels Λ(=1, 2, 4 and 8) are 6, 6, 2, and 2.[equation 1]S _(n)(Λ)=Λ·{(Y _(n) +m)mod └N _(CCE,j) ^(FDM-PDCCH) /Λ┘}+iY _(n)=(A×Y _(n-1))mod D  (Equations 1)whereN_(CCE,j) ^(FDM-PDCCH): the total number of CCEs in slot j of theenhanced PDCCH,i=0, . . . , Λ−1,m=0, . . . , M(Λ)−1,M(Λ): the number of PDCCH candidates at each aggregation level,Y⁻¹=n_(UEID)≠0A=39827, andD=65537.

<Without Cross Interleaving>

In the event of “without cross interleaving,” the base station apparatuseNB allocates DCI for each mobile terminal apparatus UE, to an enhancedPDCCH, in PRB units. For example, the base station apparatus eNBdetermines the aggregation level, which shows the number of VRBs toallocate continuously, based on the received quality reported from eachmobile terminal apparatus UE. Then, to the enhanced PDCCH, a number ofVRBs to match the aggregation level of each mobile terminal apparatus UEare allocated as radio resources of the DCI for each mobile terminalapparatus UE.

In the event of “without cross interleaving,” radio resources areallocated to the enhanced PDCCH, as radio resources of the DCI for eachmobile terminal apparatus UE, in PRB units. In radio resources where theenhanced PDCCH may be arranged, DM-RSs, which are user-specific downlinkreference signals, are arranged. Consequently, it is possible todemodulate the enhanced PDCCH using the DM-RSs. In this case, channelestimation is possible in PRB units, so that it is possible toeffectively execute beam forming for each mobile terminal apparatus UE.

The mobile terminal apparatus UE monitors a plurality of enhanced PDCCHcandidates that may be configured by higher layer signals. The mobileterminal apparatus UE is not reported the VRBs of the enhanced PDCCHwhere the DCI for the mobile terminal apparatus UE is allocated, and theselected aggregation level. Consequently, enhanced PDCCH decoding isexecuted for all the VRBs of the enhanced PDCCH signal where the DCI forthe mobile terminal apparatus UE may be allocated.

Also, to minimize the number of times the mobile terminal apparatus UEtries blind decoding, the base station apparatus eNB sets a search spacefor every mobile terminal apparatus UE, and is able to allocate VRBs forthe DCI for each mobile terminal apparatus UE in this search space. Inthis case, the mobile terminal apparatus UE tries to decode the DCI inthe corresponding search space (see FIG. 6).

When trying blind decoding in the search space, the mobile terminalapparatus UE is able to determine the search space by the followingequation 2, according to each aggregation level (VRB units). Note thatthe numbers of PDCCH candidates to correspond to individual aggregationlevels Λ (=1, 2, 4, 8) are 6, 6, 2, and 2. Although a case is shown herewhere the aggregation level is 6, 6, 2 or 2, obviously, the aggregationlevel and the number of PDCCH candidates are not limited to these.[equation 2]n _(VRB) ^(FDM-PDCCH)=(Λ·m+i)mod N _(VRB) ^(FDM-PDCCH)  (Equation 2)wherei=0, . . . , Λ−1,m=0, . . . , M(Λ)−1,M(Λ): the number of PDCCH candidates at each aggregation level, andN_(VRB) ^(FDM-PDCCH): the number of VRBs to set in the enhanced PDCCH.

For example, when eight (N_(VRB)=8) VRB sets are arranged as an enhancedPDCCH in the resource allocation type 0 in a cell bandwidth formed withtwenty-five PRBs, the VRBs are numbered by VRB indices, in order, fromthe smallest PRB index (RBG index) (see FIG. 6).

At aggregation level 1, six search spaces are set in VRBs #0 to #5. Ataggregation level 2, four search spaces are set in VRBs #0 to #7, intwo-VRB units. At aggregation level 4, two search spaces are set in VRBs#0 to #7, in four-VRB units. At aggregation level 8, one search space isset in VRBs #0 to #7, in eight-VRB units. Note that, at aggregationlevels 2 and 8, search spaces overlap due to shortage of the number ofVRBs.

Then, in the mobile terminal apparatus UE, the search spaces are subjectto blind decoding according to the aggregation level, and the DCIallocated to the VRBs is acquired. In this way, in the event of “withoutcross interleaving,” each user's DCI is allocated in PRB units, andsubject to blind decoding in the search space defined by VRB indices.

In this way, by using an enhanced PDCCH (FDM-type PDCCH) as a controlchannel region, it is possible to secure downlink control channelcapacity. Also, by limiting the search spaces, it is possible to reducethe number of times the mobile terminal apparatus UE tries blinddecoding.

According to a second aspect of the present invention, the aggregationlevels that can be used for the PDCCH and the FDM-type PDCCH, and theDCI format types, are limited. By this means, it is possible to reducethe number of times of blind decoding or improve characteristicsaccording to the environment.

The number of times the mobile terminal apparatus UE tries blinddecoding is based on the numbers of PDCCH candidates (6, 6, 2 and 2)corresponding to individual aggregation levels Λ (=1, 2, 4 and 8). Forexample, when the numbers of search spaces to correspond to theaggregation levels Λ (=1, 2, 4 and 8) are (6, 6, 2 and 2), respectively,the mobile terminal apparatus UE tries blind decoding sixteen times(=6+6+2+2) to decode the conventional

PDCCH, and tries blind decoding sixteen times to decode the FDM-typePDCCH. Consequently, when the PDCCH and the FDM-type PDCCH are usedtogether, compared to the case of using the PDCCH and the FDM-typePDCCH, the number of times the mobile terminal apparatus UE tries blinddecoding increases.

Then, the aggregation level is limited such that the aggregation level Λvaries between the PDCCH and the FDM-type PDCCH. For example, the PDCCHaggregation level is limited to four or eight, and the aggregation levelof the FDM-type PDCCH is limited to one or two. By this means, as thenumber of times of blind decoding in the mobile terminal apparatus UE,blind decoding is performed four times for the PDCCH (=2+2), and blinddecoding is performed twelve times for the FDM-type PDCCH (=6+6).Consequently, even when the PDCCH and the FDM-type PDCCH are usedtogether, it is possible to keep the number of times the mobile terminalapparatus UE tries blind decoding to sixteen times (=4+12). This is thesame number of times as the total number of times the mobile terminalapparatus UE tries blind decoding when the PDCCH and the FDM-type PDCCHare not used together.

Note that the limit of the aggregation level for the PDCCH and theFDM-type PDCCH is not limited to the above case. For example, it isequally possible to determine the limit of the aggregation level suchthat the number of users to multiplex is maximized, and determine thelimit of the aggregation level such that the improvement of performanceof cell edge users is given priority.

The mobile terminal apparatus UE is reported the limit of theaggregation level with respect to the PDCCH and the FDM-type PDCCH inadvance. When the aggregation levels of the PDCCH and the FDM-type PDCCHare limited, the number of times of blind decoding is limited accordingto the limited aggregation levels, so that the mobile terminal apparatusUE is able to reduce the total number of times of blind decoding.

Also, the DCI format type is limited such that the DCI format variesbetween the PDCCH and the FDM-type PDCCH. For example, the PDCCH islimited to transmission of DCI for downlink scheduling allocation (forexample, DCI formats 1A, 2 and so on), and the FDM-type PDCCH is limitedto transmission of DCI for an uplink grant (for example, DCI formats 0and 4). Note that the combination of the DCI formats for the PDCCH andthe FDM-type PDCCH is not limited to this.

By this means, the mobile terminal apparatus UE demodulates the DCI fordownlink scheduling allocation earlier in time, so that it is possibleto start demodulating the PDSCH right after the PDCCH that is receivedearlier in time than the FDM-type PDCCH is decoded.

It is also possible to provide a configuration in which theabove-described limit of the aggregation level and the limit of the DCIformat are reported from the base station apparatus eNB to the mobileterminal apparatus UE using higher layer signaling and the settings ofthe above limits are switched dynamically. By this means, flexiblesystem operation is made possible.

According to a third aspect of the present invention, the DCI type ofeach slot is limited such that a plurality of DCIs of the same bit sizeare arranged in one of the first-half slot and the second-half slot of aPRB where the FDM-type PDCCH is allocated. By this means, the number oftimes to try blind decoding in the mobile terminal apparatus UE isreduced, so that it is possible to reduce the load of the mobileterminal apparatus UE.

For example, in the R-PDCCH defined in LTE-A (Rel. 10), downlinkscheduling allocation DCI (for example, DCI formats 1A, 2A and so on) isarranged in the first-half slot, and uplink grant DCI (for example, DCIformats 0, 4 and so on) is arranged in the second-half slot. FIG. 7A isa schematic diagram of a DCI arrangement where the allocation of DCI forthe R-PDCCH is employed as is in the FDM-type PDCCH resource blockproposed by the present inventors.

In this case, the bit size varies between DCI formats 1A and 2A, so thatblind decoding becomes necessary individually. Also, the bit size variesbetween DCI formats 0 and 4, so that separate blind decoding isnecessary. Consequently, for example, when the numbers of search spacescorresponding to aggregation levels Λ (=1, 2, 4 and 8) are 6, 6, 2 and2, respectively, the mobile terminal apparatus UE tries blind decodingsixteen times (=6+6+2+2) for DCI format 1A arranged in the first-halfslot. Likewise, blind decoding is tried sixteen times, for each of DCIformat 2A arranged in the first-half slot, DCI format 0 arranged in thesecond-half slot, and DCI format 4 arranged in the second-half slot.Consequently, the total number of times the mobile terminal apparatus UEtries blind decoding is 16×4 times (sixty-four times).

On the other hand, FIG. 7B shows an example of limiting the DCI formatsuch that a plurality of DCIs of the same bit size are arranged in thefirst-half slot. As shown in FIG. 7B, DCI format 0 for an uplink grant,which is arranged in the second-half slot in FIG. 7A, is re-arranged inthe first-half slot. DCI format 0 is the same bit size as DCI format 1Afor downlink scheduling allocation arranged in the first-half slot.

In this case, since DCI formats 1A and 0 arranged in the first-half slotare the same bit size, so that the mobile terminal apparatus UE is ableto decode these at the same time by one blind decoding (maximum sixteentimes). Blind decoding is tried sixteen times for each of DCI format 2Aarranged in the first-half slot and DCI format 4 arranged in thesecond-half slot. Consequently, the number of times the mobile terminalapparatus UE tries blind decoding is 16×3 times (48 times).Consequently, the number of times to try blind decoding in the mobileterminal apparatus UE is reduced, so that it is possible to reduce theload of the mobile terminal apparatus UE. Note that DCI format 1A andDCI format 0 are distinguished by processing the top one bit, afterblind decoding is tried sixteen times.

Note that it is possible to provide a configuration in which DCI format1A arranged in the first-half slot in FIG. 7A is arranged in thesecond-half slot. In this case, DCI formats 0 and 1A of the same bitsize are arranged in the second-half slot. In this case, the number oftimes the mobile terminal apparatus UE tries blind decoding is 16×3times (forty-eight times). Note that the combination of DCI formats ofthe same message size in the FDM-type PDCCH resource blocks is notlimited to the above example.

According to a fourth aspect of the present invention, a search spaceconfiguration in the event of cross-carrier scheduling is applied to theFDM-type PDCCH is provided.

In LTE-A (Rel-10), fundamental frequency blocks to match the system bandup to LTE (Rel. 8) are referred to as component carriers (CCs), andthere is an agreement to realize broadbandization by aggregating aplurality of CCs. A communication environment where part of the CCsreceives strong interference from other cells and other CCs are lessinfluenced by interference may be provided. So, a mechanism to allocateDCI for a shared data channel (PDSCH and so on) that is transmitted fromother CCs that receive strong interference from other cells, from otherCCs where the influence of interference is less, is under study. Here,sending the PDCCH of a CC to transmit the PDSCH from another CC besidesthat CC is referred to as cross-carrier scheduling.

FIG. 8 is a conceptual diagram where cross-carrier scheduling isapplied. With the method shown in FIG. 8, cross-carrier scheduling,where the PDCCH for the PDSCH sensed in the CC (secondary cell) is sentfrom another CC (primary cell) besides that CC (secondary cell), isadopted. To be more specific, DCI-1 for allocating the PDSCH or PUSCH ofCC #1 is allocated to the PDCCH of CC #1, and DCI-2 for allocating thePDSCH or PUSCH of CC #2 is allocated to the PDCCH of different CC #1. Athree-bit CIF (Carrier Indicator Field) to indicate the CC of thescheduling target, is attached to each DCI. The mobile terminalapparatus UE is able to determine to which CC the PDSCH is allocated,based on the CIF value attached to demodulated DCI.

With the present invention, search spaces are configured such that twosearch spaces of the FDM-type PDCCH for allocating the PDSCH of theprimary cell and the FDM-type PDCCH for allocating the PDSCH of thesecondary cell, allocated to the same CC (primary cell) by cross-carrierscheduling, continue. FIG. 9 shows a case where the search space of CC#1 to be the primary cell and the search space of CC #2 to be thesecondary cell become a continuous configuration.

In this way, by the search space configuration in which the searchspaces of the primary cell and the secondary cell continue, it ispossible to prevent the search spaces of the primary cell and thesecondary cell from overlapping. By this means, it is possible to reducethe possibility that the DCI to allocate the PDSCH between different CCsfrom being blocked.

When the method of allocating DCI to the FDM-type PDCCH is “with crossinterleaving,” it is possible to find the starting position of thesearch space in subframe n by the following equations 3. Note that thenumbers of FDM-type PDCCH candidates corresponding to aggregation levelsΛ (=1, 2, 4 and 8) are 6, 6, 2 and 2, respectively.[equation 3]S _(n)(Λ)=Λ·{(Y _(n) +m+n _(CI) M(Λ))mod └N _(CCE,j) ^(FDM-PDCCH) /Λ┘}+iY _(n)=(A×Y _(n-1))mod D  (Equations 3)whereN_(CCE,j) ^(FDM-PDCCH): the total number of CCEs in slot j in theenhanced PDCCH,i=0, . . . , Λ−1,m=0, . . . , M(Λ)−1,n_(CI)=CIF valueM(Λ): the number of PDCCH candidates at each aggregation level,Y⁻¹=n_(UEID)≠0,A=39827, andD=65537.

Also, when the method of allocating DCI to the FDM-type PDCCH is“without cross interleaving,” DCI is allocated in PRB units, so that itis possible to determine the starting position of the search space insubframe n by the following equation 4.[equation 4]S _(n)(Λ)=Λ·{(Y _(n) +m+n _(CI) M(Λ))mod N _(VRB) ^(FDM-PDCCH)}+i  (Equation 4)

Now, a radio communication system 1 having a mobile terminal apparatus10 and a base station apparatus 20 according to an embodiment of thepresent invention will be described with reference to FIG. 10. Themobile terminal apparatus 10 and the base station apparatus 20 supportLTE-A.

As shown in FIG. 10, the radio communication system 1 is configured toinclude a base station apparatus 20, a plurality of mobile terminalapparatuses 10 that communicate with this base station apparatus 20. Thebase station apparatus 20 is connected with a higher station apparatus30, and this higher station apparatus 30 is connected with a corenetwork 40. Also, base station apparatuses 20 are connected with eachother by wire connection or by wireless connection. The mobile terminalapparatuses 10 are able to communicate with the base station apparatuses20 in cells C1 and C2. Note that the higher station apparatus 30includes, for example, an access gateway apparatus, a radio networkcontroller (RNC), a mobility management entity (MME) and so on, but isby no means limited to these.

Although each mobile terminal apparatus 10 may be either an LTE terminalor an LTE-A terminal, in the following description, simply a mobileterminal apparatus will be described, unless specified otherwise. Also,although the mobile terminal apparatus 10 performs radio communicationwith the base station apparatus 20 for ease of explanation, moregenerally, user apparatuses including mobile terminal apparatuses andfixed terminal apparatuses may be used as well.

In the radio communication system 1, as radio access schemes, OFDMA(Orthogonal Frequency Division Multiple Access) is applied to thedownlink, and SC-FDMA (Single-Carrier Frequency-Division MultipleAccess) is applied to the uplink. Note that the uplink radio accessscheme is not limited to this. OFDMA is a multi-carrier transmissionscheme to perform communication by dividing a frequency band into aplurality of narrow frequency bands (subcarriers) and mapping data toeach subcarrier. SC-FDMA is a single carrier transmission scheme toreduce interference between terminals by dividing, per terminal, thesystem band into bands formed with one or continuous resource blocks,and allowing a plurality of terminals to use mutually different bands.

Now, communication channel configurations defined in LTE-A will bedescribed. Downlink communication channels include a PDSCH that is usedby each mobile terminal apparatus 10 on a shared basis, downlink L1/L2control channels (PDCCH, PCFICH, PHICH), and an enhanced PDCCH. Userdata and higher control signals are transmitted by the PDSCH. Here,downlink control signals are multiplexed on radio resources up to apredetermined number of OFDM symbols (the first to third OFDM symbols)from the subframe top, and the enhanced PDCCH signal and the PDSCHsignal are frequency-division-multiplexed on radio resources after apredetermined number of OFDM symbols.

PDSCH and PUSCH scheduling information is transmitted by means of theenhanced PDCCH (FDM-type PDCCH). The enhanced PDCCH is used to supportthe shortage of PDCCH capacity using the resource region where the PDSCHis allocated. The higher control signals may include information relatedto the PRB positions where the enhanced PDCCH is set (for example, RBGinformation), the limits of the aggregation levels for the PDCCH and theenhanced PDCCH, the limits of DCI format types, and information relatedto the parameters to use for the control algorithm to determine thestarting position of the search space.

The uplink control channels include a PUSCH that is used by each mobileterminal apparatus 10 on a shared basis, and a PUCCH, which is an uplinkcontrol channel. User data is transmitted by means of this PUSCH.Downlink radio quality information (CQI: Channel Quality Indicator),retransmission acknowledgement signals (ACK/NACK signal) and so on aretransmitted by the PUCCH.

Referring to FIG. 11, an overall configuration of the base stationapparatus 20 according to the present embodiment will be described. Thebase station apparatus 20 has a plurality of transmitting/receivingantennas 201 for MIMO transmission, an amplifying section 202, atransmitting/receiving section (reporting section) 203, a basebandsignal processing section 204, a call processing section 205, and atransmission path interface 206.

User data to be transmitted from the base station apparatus 20 to themobile terminal apparatus 10 is input from the higher station apparatus30, into the baseband signal processing section 204, via thetransmission path interface 206. The baseband signal processing section204 performs a PDCP layer process, division and coupling of user data,RLC (Radio Link Control) layer transmission processes such as an RLCretransmission control transmission process, MAC (Medium Access Control)retransmission control, including, for example, an HARQ transmissionprocess, scheduling, transport format selection, channel coding, aninverse fast Fourier transform (IFFT) process, and a precoding process.

The baseband signal processing section 204 reports, to the mobileterminal apparatus 10, control information to allow communication in thecell, by a broadcast channel. The broadcast information forcommunication in the cell includes, for example, the uplink or downlinksystem bandwidth, identification information of a root sequence (rootsequence index) for generating random access preamble signals in thePRACH (Physical Random Access Channel), and so on.

Each transmitting/receiving section 203 converts the baseband signal,which has been subjected to precoding and is output from the basebandsignal processing section 204 per antenna, into a radio frequency band.The amplifying section 202 amplifies the radio frequency signal havingbeen subjected to frequency conversion and transmits the result from thetransmitting/receiving antennas 201. Meanwhile, as for data to betransmitted on the uplink from the mobile terminal apparatus 10 to thebase station apparatus 20, a radio frequency signal that is received ineach transmitting/receiving antenna 201 is amplified in the amplifyingsection 202, subjected to frequency conversion and converted into abaseband signal in each transmitting/receiving section 203, and is inputin the baseband signal processing section 204.

The baseband signal processing section 204 performs an FFT process, anIDFT process, error correction decoding, a MAC retransmission controlreceiving process, and RLC layer and PDCP layer receiving processes, ofthe user data that is included in the input baseband signal, and theresult is transferred to the higher station apparatus 30 via thetransmission path interface 206. The call processing section 205performs call processing such as setting up and releasing calls, managesthe state of the base station apparatus 20 and manages the radioresources.

Next, referring to FIG. 12, an overall configuration of a mobileterminal apparatus according to the present embodiment will bedescribed. An LTE terminal and an LTE-A terminal have the same hardwareconfigurations in principle parts, and therefore will be describedindiscriminately. A mobile terminal apparatus 10 has a plurality oftransmitting/receiving antennas 101 for MIMO transmission, an amplifyingsection 102, a transmitting/receiving section 103, a baseband signalprocessing section 104, and an application section 105.

As for downlink data, radio frequency signals that are received in aplurality of transmitting/receiving antennas 10 are each amplified inthe amplifying section 10, and subjected to frequency conversion andconverted into a baseband signal in the transmitting/receiving section10. This baseband signal is subjected to receiving processes such as anFFT process, error correction decoding and retransmission control, inthe baseband signal processing section 104. In this downlink data,downlink user data is transferred to the application section 10. Theapplication section 105 performs processes related to higher layershigher than the physical layer and the MAC layer. Also, in the downlinkdata, broadcast information is also transferred to the applicationsection 105.

On the other hand, uplink user data is input from the applicationsection 105 into the baseband signal processing section 104. Thebaseband signal processing section 104 performs transmission process forretransmission control (HARQ (Hybrid ARQ)), channel coding, precoding, aDFT process, an IFFT process, and so on, and the result is transferredto each transmitting/receiving section 103.

The baseband signal that is output from the baseband signal processingsection 104 is converted into a radio frequency band in thetransmitting/receiving section 103. After that, the amplifying section102 amplifies the radio frequency signal having been subjected tofrequency conversion, and transmits the result from thetransmitting/receiving antennas 101.

FIG. 13 is a functional block diagram of a baseband signal processingsection 204 provided in the base station apparatus 20 according to thepresent embodiment and part of higher layers, and primarily illustratesthe function blocks for transmission processes in the baseband signalprocessing section 204. FIG. 13 shows an example of a base stationconfiguration which can support the maximum number of component carriersM (CC #0 to CC #M). Transmission data for the mobile terminal apparatus10 under the base station apparatus 20 is transferred from the higherstation apparatus 30 to the base station apparatus 20.

Control information generating sections 300 generate higher controlinformation for performing higher layer signaling (for example, RRCsignaling), on a per user basis. Also, the higher control informationmay include resource allocation signal (PRB positions) where an enhancedPDCCH (FDM-type PDCCH) can be mapped in advance. Also, informationrelated to parameters used for the control algorithm to determine thestarting position of a search space, and information related to thelimit of aggregation levels or the limit of DCI format types.

The data generating section 301 outputs transmission data transferredfrom the higher station apparatus 30 as user data separately. Thecomponent carrier selection section 302 selects, on a per user basis,component carriers to use for radio communication with the mobileterminal apparatus 10. An increase/decrease of component carriers isreported from the base station apparatus 20 to the mobile terminalapparatus 10 by RRC signaling, and a message of completion is receivedfrom the mobile terminal apparatus 10.

The scheduling section 310 controls the assignment of component carriersto a mobile terminal apparatus 10 in communication with them accordingto overall communication quality of the system band. Also, from thecomponent carriers that are selected on a per mobile terminal apparatusbasis, a specific component carrier (PCC) is determined. Also, thescheduling section 310 controls the allocation of resources in componentcarriers CC #1 to CC #M. LTE users and LTE-A users are scheduledseparately. The scheduling section 310 receives the transmission dataand retransmission command from the higher station apparatus 30, andalso receives the channel estimation values and CQI of resource blockfrom the receiving section having measured an uplink received signal.

Also, the scheduling section 310 schedules uplink and downlink controlinformation and uplink and downlink shared channel signals withreference to the retransmission commands, channel estimation values andCQIs that are inputted. A propagation path in mobile communicationvaries differently per frequency, due to frequency selective fading. So,the scheduling section 310 designates resource blocks (mappingpositions) of good communication quality, on a per subframe basis, withrespect to the user data for each mobile terminal apparatus 10 (which isreferred to as “adaptive frequency scheduling”). In adaptive frequencyscheduling, a mobile terminal apparatus 10 having good propagation pathquality is selected for each resource block. Consequently, thescheduling section 310 designates resource blocks (mapping positions),using the CQI of each resource block, fed back from each mobile terminalapparatus 10.

Likewise, the scheduling section 310 designates resource blocks (mappingpositions) of good communication quality, on a per subframe basis, withrespect to control information transmitted by the enhanced PDCCH, byadaptive frequency scheduling. Consequently, the scheduling section 310designates resource blocks (mapping positions) using the CQI of eachresource block, fed back from each mobile terminal apparatus 10.

Also, the scheduling section 310 controls the aggregation levelaccording to the conditions of the propagation path with the mobileterminal apparatus 10. As for the PDCCH, the CCE aggregation level iscontrolled, and, as for the enhanced PDCCH, the CCE aggregation level(in the event of “with cross interleaving”) or the VRB aggregation level(in the event of “without cross interleaving”) is controlled. Note that,when the aggregation levels are limited in the PDCCH and the enhancedPDCCH, the aggregation levels are controlled within a range for theaggregation levels. For example, the aggregation levels for the PDCCHare limited to four and eight, and the aggregation levels for theenhanced PDCCH are limited to one and two. For cell edge users, the CCEaggregation level and the VRB aggregation level are increased. Also, theMCS (coding rate and modulation scheme) that fulfills a predeterminedblock error rate with the allocated resource blocks is determined.Parameters to fulfill the MCS (coding rate and modulation scheme)determined by the scheduling section 310 are set in the channel codingsections 303, 308 and 312, and in the modulation sections 304, 309 and313.

The baseband signal processing section 204 has channel coding sections303, modulation sections 304, and mapping sections 305, to match themaximum number of users to be multiplexed, N, in one component carrier.The channel coding sections 303 perform channel coding of the downlinkshared data channel (PDSCH), which is formed with user data (includingpart of higher control signals) that is output from the data generatingsections 301, on a per user basis. The modulation sections 304 modulateuser data having been subjected to channel coding, on a per user basis.The mapping sections 305 map the modulated user data to radio resources.

Also, the baseband signal processing section 204 has generating sectionsthat generate control information using a predetermined DCI format froma plurality of DCI formats (downlink control information generatingsections 306 and uplink control information generating sections 311).The plurality of DCI formats include a DCI format having an uplink grantas its content (for example, DCI format 0/4), and a DCI format havingdownlink scheduling allocation as its content (for example, DCI format1A and so on). The scheduling section 310 is able to limit the DCIformats to apply to the PDCCH and the enhanced PDCCH for the downlinkcontrol information generating sections 306 and uplink controlinformation generating sections 311. For example, the scheduling section310 apply only downlink DCI formats (1A, 2 and so on) to the PDCCH on alimited basis, and apply only uplink DCI formats (0, 4 and so on) to theenhanced PDCCH on a limited basis. Also, regarding the enhanced PDCCH,the scheduling section 310 executes control such that a plurality of DCIformats of the same bit size are arranged in the first-half slot or thesecond-half slot in the time domain.

The downlink control information generating section 306 generatesdownlink shared data channel control information for controlling thePDSCH, using DCI formats having downlink scheduling allocation as itscontent (for example, DCI format 1A and so on). At this time, thedownlink shared data channel control information is generated per user.Also, the downlink shared data channel control information contains anidentification field (CIF) which identifies the uplink serving cellwhere the PDSCH is allocated. The scheduling section 310 determines thesearch space starting position based on the CIF value, whencross-carrier scheduling is applied. In the event of “with crossinterleaving,” the scheduling section 310 sets the search space based onthe search space starting position calculated by the equations (3), and,in the event of “without cross interleaving,” the scheduling section 310sets the search space based on the search space starting positioncalculated by the equation (4). Also, the baseband signal processingsection 204 has a downlink shared channel control information generatingsection 307 which generates downlink shared control channel controlinformation, which is downlink control information that is commonbetween users.

The uplink control information generating section 311 generates uplinkdata channel control information for controlling the PUSCH using DCIformats having an uplink grant as its content (for example, DCI format0/4). The uplink shared data channel control information is generated ona per user basis. Also, the uplink shared data channel controlinformation contains an identification field (CIF), which identifies theuplink serving cell where the PUSCH is allocated. Also, the basebandsignal processing section 204 has a channel coding section 312 thatperforms channel coding of generated uplink shared data channel controlinformation on a per user basis, and a modulation section 313 whichmodulates the uplink shared data channel control information having beensubjected to channel coding on a per user basis.

The cell-specific reference signal generating section 318 generates acell-specific reference signal (CRS). The cell-specific reference signal(CRS) is multiplexed on radio resources of the above PDCCH region andtransmitted. Also, the user-specific reference signal generating section320 generates a downlink demodulation reference signal (DM-RS). Theuser-specific downlink demodulation reference signal (DM-RS) ismultiplexed on the radio resources of the above PDSCH region andtransmitted.

Control information that is modulated on a per user basis in the abovemodulation sections 309 and 313 is multiplexed by a control channelmultiplexing section 314. Downlink control information for the PDCCH ismultiplexed on the first to third OFDM symbols from a top symbol of thesubframe, and is interleaved in an interleaving section 315. Meanwhile,downlink control information for the enhanced PDCCH (FRM-type PDCCH) isfrequency-division-multiplexed on radio resources after a predeterminednumber of symbols in the subframe, and is mapped to resource blocks(PRBs) in a mapping section 319. In this case, the mapping section 319performs the mapping based on commands from the scheduling section 310.Note that the mapping section 319 may perform mapping by adopting “withcross interleaving,” in addition to “without cross interleaving.”

The precoding weight multiplying section 321 controls (shifts) the phaseand/or amplitude of the transmission data and user-specific demodulationreference signals (DM-RSs) that are mapped to the subcarriers, for eachof a plurality of antennas. The transmission data and user-specificdemodulation reference signals (DM-RSs) having been subjected to a phaseand/or amplitude shift in the precoding weight multiplying section 321are output to an IFFT section 316.

The IFFT section 316 receives as input control signals from theinterleaving section 315 and the mapping section 318, and receives asinput user data from the mapping section 305. The IFFT section 316converts the downlink channel signal from a frequency domain signal intoa time sequence signal by an inverse fast Fourier transform. A cyclicprefix inserting section 317 inserts cyclic prefixes in the timesequence signal of the downlink channel signal. Note that a cyclicprefix functions as a guard interval for cancelling the differences inmultipath propagation delay. The transmission data to which cyclicprefixes have been added, is transmitted to the transmitting/receivingsection 203.

FIG. 14 is a functional block diagram of the baseband signal processingsection 104 provided in a user terminal 10 and is a function block of anLTE-A terminal which supports LTE-A.

A downlink signal that is received as received data from the radio basestation apparatus 20 has the CPs removed in a CP removing section 401.The downlink signal, from which the CPs have been removed, is input inan FFT section 402. The FFT section 402 performs a fast Fouriertransform (FFT) on the downlink signal, converts the time domain signalinto a frequency domain signal and inputs this signal in a demappingsection 403. The demapping sections 403 demaps the downlink signal, andextracts, from the downlink signal, multiplex control information inwhich a plurality of pieces of control information are multiplexed, userdata and higher control signals. Note that the demapping process by thedemapping section 403 is performed based on higher control signals thatare received as input from the application section 105. The multiplexcontrol information output from the demapping section 403 isdeinterleaved in a deinterleaving section 404. Note that it is alsopossible to provide a configuration in which the enhanced PDCCH signalthat is not interleaved is input as is in a control informationdemodulation section 405, without involving the de-interleaving section404.

Also, the baseband signal processing section 104 has a controlinformation demodulation section 405 that demodulates controlinformation, a data demodulation section 406 that demodulates downlinkshared data, and a channel estimation section 407. The controlinformation demodulation section 405 has a shared control channelcontrol information demodulation section 405 a that demodulates downlinkshared control channel control information from multiplex controlinformation, an uplink shared data channel control informationdemodulation section 405 b that demodulates uplink shared data channelcontrol information from multiplex control information, and a downlinkshared data channel control information demodulation section 405 c thatdemodulates downlink shared data channel control information frommultiplex control information. The data demodulation section 406 has adownlink shared data demodulation section 406 a that demodulates userdata and higher control signals, and a downlink shared channel datademodulation section 406 b that demodulates downlink shared channeldata.

The shared control channel control information demodulation section 405a extracts shared control channel control information, which is controlinformation that is common between users, by the blind decoding process,demodulation process, channel decoding process and so on of the commonsearch space of the downlink control channel (PDCCH). The shared controlchannel control information includes downlink channel qualityinformation (CQI), and therefore is input in a mapping section 415 andmapped as part of transmission data for the base station apparatus 20.

The uplink shared data channel control information demodulation section405 b extracts uplink shared data channel control information (forexample, UL grant) by the blind decoding process, demodulation process,channel decoding process and so on of the user-specific search space ofthe downlink control channel (PDCCH). The demodulated uplink shared datachannel control information is input in the mapping section 415 and isused to control the uplink shared data channel (PUSCH).

The downlink shared data channel control information demodulationsection 405 c extracts user-specific downlink shared data channelcontrol information (for example, DL assignment) by the blind decodingprocess, demodulation process, channel decoding process and so on of theuser-specific search space of the downlink control channel (PDCCH). Thedemodulated downlink shared data channel control information is input inthe downlink shared data demodulation section 406 a, is used to controlthe downlink shared data channel (PDSCH), and is input in the downlinkshared data demodulating section 406 a.

The control information demodulation section 405 demodulates the PCFICHfrom the top symbol of a subframe and specifies the control region wherethe PDCCH is arranged, and demodulates the PDCCH from the specifiedcontrol region. Also, the control information demodulation section 405demodulates the enhanced PDCCH that is frequency-division-multiplexed inradio resources (data region) from the next symbol of the control regionto the last symbol of the subframe.

When cross-carrier scheduling is applied, the control informationdemodulation section 405 calculates the search space starting positionby the equations 3 in the event of “with cross interleaving,” andperforms blind decoding of the search space specified based on thecalculated search space starting position. Also, in the event of“without cross interleaving,” the control information demodulationsection 405 calculates the search space starting position by theequation 4 and performs blind decoding of the search space specifiedbased on the calculated search space starting position.

Note that blind decoding is performed in CCE units with respect to theenhanced PDCCH and PDCCH where “with cross interleaving” applies, andblind decoding is performed in VRB units with respect to the enhancedPDCCH and PDCCH where “without cross interleaving” applies.

When information about the limits of the aggregation levels for theenhanced PDCCH and the PDCCH is reported, the control informationdemodulation section 405 executes blind decoding according to eachaggregation level limited for the enhanced PDCCH and the PDCCH. Also,when downlink DCI (formats 1A, 2 and so on) is allocated to the PDCCHand uplink DCI (formats 0, 4 and so on) is allocated to the enhancedPDCCH, the downlink DCI is demodulated from the PDCCH and the uplink DCIis demodulated from the enhanced PDCCH. As for the enhanced PDCCH, whena plurality of DCI formats of the same bit size are arranged in thefirst-half slot or the second-half slot, the DCI formats of the same bitsize are demodulated at the same time by one blind decoding.

The downlink shared data modulation section 406 a acquires user data andhigher control information based on downlink shared data channel controlinformation input from the downlink shared data channel controlinformation demodulation section 405 c. The PRB positions (VRBpositions) where the enhanced PDCCH can be mapped included in the highercontrol information are output to the downlink shared data channelcontrol information demodulation section 405 c. The downlink sharedchannel data demodulation section 406 b demodulates downlink sharedchannel data based on uplink shared data channel control informationthat is input from the uplink shared data channel control informationdemodulation section 405 b.

The channel estimation section 407 performs channel estimation using auser-specific reference signal (DM-RS) or a cell-specific referencesignal (CRS). When demodulating the normal PDCCH and the enhanced PDCCH“with cross interleaving,” channel estimation is performed using acell-specific reference signal. On the other hand, when demodulating theenhanced PDCCH and user data “without cross interleaving,” channelestimation is performed using the DM-RS and CRS. The estimated channelvariation is output to the shared control channel control informationdemodulation section 405 a, the uplink shared data channel controlinformation demodulation section 405 b, the downlink shared data channelcontrol information demodulation section 405 c and the downlink shareddata demodulation section 406 a. In these demodulation sections,demodulation processes are performed using the estimated channelvariation and demodulation reference signal.

The baseband signal processing section 104 has, as function blocks ofthe transmission processing system, a data generating section 411, achannel coding section 412, a modulation section 413, a DFT section 414,a mapping section 415, an IFFT section 416, and an CP inserting section417. The data generating section 411 generates transmission data frombit data that is received as input from the application section 105. Thechannel coding section 412 applies channel coding processes such aserror correction to the transmission data, and the modulation section413 modulates the transmission data having been subjected to channelcoding by QPSK and so on.

The DFT section 414 performs a discrete Fourier transform on themodulated transmission data. The mapping section 415 maps the frequencycomponents of the data symbol after the DFT, to the subcarrier positionsdesignated by the base station apparatus 20. The IFFT section 416converts the input data to match the system band into time sequence databy performing an inverse fast Fourier transform, and the CP insertingsection 417 inserts cyclic prefixes in the time sequence data in dataunits.

The present invention is by no means limited to the above embodimentsand can be implemented in various modifications. Regarding the sizes andshapes illustrated in the accompanying drawings in relationship to theabove embodiments, these are by no means limiting, and can be changed asappropriate within a range the effect of the present invention issufficiently provided. Besides, the present invention can be implementedwith various changes, without departing from the scope of the presentinvention.

The disclosure of Japanese Patent Application No. 2011-103223, filed onMay 2, 2011, including the specification, drawings and abstract, isincorporated herein by reference in its entirety.

The invention claimed is:
 1. A radio base station apparatus comprising:a signal generator that generates a first downlink control signal to betransmitted to a mobile terminal apparatus by a physical downlinkcontrol channel and a second downlink control signal to be transmittedto the mobile terminal apparatus by an enhanced physical downlinkcontrol channel; a control channel multiplexer that multiplexes thefirst downlink control signal on a radio resource of first n symbols(n=1, 2, or 3) allocated to the physical downlink control channel in asubframe and frequency-division-multiplexes the second downlink controlsignal on a radio resource which is allocated to the enhanced physicaldownlink control channel and has predetermined symbols in a time domainfollowing the symbols where the first downlink control signal ismultiplexed in the subframe; a transmitter that transmits the firstdownlink control signal by the physical downlink control channel and thesecond downlink control signal by the enhanced physical downlink controlchannel; and a scheduler that controls an aggregation level of controlchannel elements to allocate to the physical downlink control channelfor the first downlink control signal and controls an aggregation levelof control channel elements to allocate to the enhanced physicaldownlink control channel for the second downlink control signal, whereinaggregation levels configurable for the physical downlink controlchannel or the enhanced physical downlink control channel are limited tomake some of the aggregation levels configurable for one of the physicaldownlink control channel and the enhanced physical downlink controlchannel and unconfigurable for the other.
 2. The radio base stationapparatus according to claim 1, wherein a format type for each of afirst-half slot and a second-half slot of the radio resource to whichthe enhanced physical downlink control channel is allocated is limitedsuch that a plurality of DCI formats of a same bit size are arranged inat least one of the first-half slot and the second-half slot.
 3. Theradio base station apparatus according to claim 1, wherein DCI (DownlinkControl Information) formats applicable to the first downlink controlsignal and the second downlink control signal are limited to make someof the DCI formats applicable to one of the first downlink controlsignal and the second downlink control signal and unapplicable to theother.
 4. The radio base station apparatus according to claim 3, whereinthe first downlink control signal is limited to a DCI format fordownlink scheduling assignment and the second downlink control signal islimited to a DCI format for an uplink grant.
 5. The radio base stationapparatus according to claim 4, wherein the radio base station apparatusnotifies the mobile terminal apparatus of information about limits forthe DCI formats applied to the first downlink control signal and thesecond downlink control signal by higher layer signaling.
 6. A mobileterminal apparatus comprising: a receiver that receives a first downlinkcontrol signal that is multiplexed on a radio resource of first nsymbols (n=1, 2, or 3) allocated to a physical downlink control channelin a subframe and a second downlink control signal that isfrequency-division-multiplexed on radio resource which is allocated toan enhanced physical downlink control channel and has predeterminedsymbols in a time domain following the symbols where the first downlinkcontrol signal is multiplexed in the subframe; and a demodulator thatperforms blind decoding on the first downlink control signal multiplexedon the radio resource allocated to the physical downlink control channelby a configured aggregation level to detect the first downlink controlchannel and to perform blind decoding on the second downlink controlsignal multiplexed on the radio resource allocated to the enhancedphysical downlink control channel by a configured aggregation level todetect the second downlink control channel, aggregation levelsconfigurable for the physical downlink control channel or the enhancedphysical downlink control channel being limited, to make some of theaggregation levels configurable for one of the physical downlink controlchannel and the enhanced physical downlink control channel andunconfigurable for the other.
 7. The mobile terminal apparatus accordingto claim 6, wherein: DCI (Downlink Control Information) formatsapplicable to the first downlink control signal and the second downlinkcontrol signal are limited to make some of the DCI formats applicable toone of the first downlink control signal and the second downlink controlsignal and unapplicable to the other, and the demodulator decodes thefirst downlink control signal limited to a DCI format for downlinkscheduling assignment earlier in time, and, after that, decodes thesecond downlink control signal limited to a DCI format for an uplinkgrant.
 8. The mobile terminal apparatus according to claim 6, wherein:the receiver receives the second downlink control signal of which aformat type is limited such that a plurality of DCI formats of a samebit size are arranged in at least either of a first-half slot and asecond-half slot of the radio resource to which the enhanced physicaldownlink control channel is allocated; and the demodulator performsblind decoding of the plurality of DCI formats of the same bit size inat least either of the first-half slot and the second-half slot in onetime.
 9. A radio communication system in which a first downlink controlsignal, a second downlink control signal and a downlink data signalgenerated in a radio base station apparatus are transmitted to a mobileterminal apparatus, and, the first and second downlink control signalsare demodulated in the mobile terminal apparatus, the radio base stationapparatus comprising: a signal generator that generates the firstdownlink control signal to be transmitted to the mobile terminalapparatus by a physical downlink control channel and the second downlinkcontrol signal to be transmitted to the mobile terminal apparatus by anenhanced physical downlink control channel; a control channelmultiplexer that multiplexes the first downlink control signal on aradio resource of first n symbols (n=1, 2, or 3) allocated to thephysical downlink control channel in a subframe andfrequency-division-multiplexes the second downlink control signal on aradio resource which is allocated to the enhanced physical downlinkcontrol channel and has predetermined symbols in a time domain followingthe symbols where the first downlink control signal is multiplexed inthe subframe; a transmitter that transmits the first downlink controlsignal by the physical downlink control channel and the second downlinkcontrol signal by the enhanced physical downlink control channel; and;and a scheduler that controls an aggregation level of control channelelements to allocate to the physical downlink control channel for thefirst downlink control signal and controls an aggregation level ofcontrol channel elements to allocate to the enhanced physical downlinkcontrol channel for the second downlink control signal, whereinaggregation levels configurable for the physical downlink controlchannel or the enhanced physical downlink control channel are limited tomake some of the aggregation levels configurable for one of the physicaldownlink control channel and the enhanced physical downlink controlchannel and unconfigurable for the other; and the mobile terminalapparatus comprising: a receiver that receives the first downlinkcontrol signal that is multiplexed on a radio resource of first nsymbols (n=1, 2, or 3) allocated to the physical downlink controlchannel in a subframe and the second downlink control signal that isfrequency-division-multiplexed on radio resource which is allocated tothe enhanced physical downlink control channel and has predeterminedsymbols in a time domain following the symbols where the first downlinkcontrol signal is multiplexed in the subframe; and a demodulator thatperforms blind decoding on the first downlink control signal multiplexedon the radio resource allocated to the physical downlink control channelby a configured aggregation level to detect the first downlink controlchannel and to perform blind decoding on the second downlink controlsignal multiplexed on the radio resource allocated to the enhancedphysical downlink control channel by a configured aggregation level todetect the second downlink control channel, aggregation levelsconfigurable for the physical downlink control channel or the enhancedphysical downlink control channel being limited, to make some of theaggregation levels configurable for one of the physical downlink controlchannel and the enhanced physical downlink control channel andunconfigurable for the other.
 10. A radio communication methodcomprising the steps of: generating a first downlink control signal tobe transmitted to a mobile terminal apparatus by a physical downlinkcontrol channel and a second downlink control signal to be transmittedto the mobile terminal apparatus by an enhanced physical downlinkcontrol channel; multiplexing the first downlink control signal on aradio resource of first n symbols (n=1, 2, or 3) allocated to thephysical downlink control channel in a subframe andfrequency-division-multiplexing the second downlink control signal on aradio resource which is allocated to the enhanced physical downlinkcontrol channel and has predetermined symbols in a time domain followingthe symbols where the first downlink control signal is multiplexed inthe subframe; transmitting the first downlink control signal by thephysical downlink control channel and the second downlink control signalby the enhanced physical downlink control channel; and controlling anaggregation level of control channel elements to allocate to thephysical downlink control channel for the first downlink control signaland controlling an aggregation level of control channel elements toallocate to the enhanced physical downlink control channel for thesecond downlink control signal, wherein aggregation levels configurablefor the physical downlink control channel or the enhanced physicaldownlink control channel are limited to make some of the aggregationlevels configurable for one of the physical downlink control channel andthe enhanced physical downlink control channel and unconfigurable forthe other.
 11. A radio communication method comprising the steps of:receiving a first downlink control signal that is multiplexed on a radioresource of first n symbols (n=1, 2, or 3) allocated to a physicaldownlink control channel in a subframe and a second downlink controlsignal that is frequency-division-multiplexed on a radio resource whichis allocated to an enhanced physical downlink control channel and haspredetermined symbols in a time domain following the symbols where thefirst downlink control signal is multiplexed in the subframe; performingblind decoding on the first downlink control signal multiplexed on theradio resource allocated to the physical downlink control channel by aconfigured aggregation level to detect the first downlink controlchannel and performing blind decoding on the second downlink controlsignal multiplexed on the radio resource allocated to the enhancedphysical downlink control channel by a configured aggregation level todetect the second downlink control channel, aggregation levelsconfigurable for the physical downlink control channel or the enhancedphysical downlink control channel being limited to make some of theaggregation levels configurable for one of the physical downlink controlchannel and the enhanced physical downlink control channel andunconfigurable for the other.